Project Summary Whooping cough, caused by Bordetella pertussis, is one of the most contagious of all contagious diseases, and the least well controlled of all vaccine preventable pediatric diseases. Since switching to acellular pertussis (aP) vaccines, incidence in the US and other countries that made this vaccine substitution, have seen incidence rates rise. Epidemiologic and experimental data suggest that a key limitation of aP vaccines is that they do not block asymptomatic carriage and spread. However, the existence of an asymptomatic carrier state for B. pertussis has never been proven, but this is because the question has never before been asked in an appropriately designed, longitudinal, cohort study, with systematic sample and symptoms collection over time. In a previous birth cohort study, the Southern Africa Mother Infant Pertussis Study, we collected ~20,000 nasopharyngeal (NP) swabs from 2000 Zambian mother/infant pairs, from birth through 14 weeks of age, with symptoms catalogued in parallel. Preliminary analysis of this set suggests that pertussis is common among the infants. Moreover, nearly all of the mothers of the infected infants were also infected with pertussis, though few showed any symptoms. This is presumptive evidence of asymptomatic carriage, but rests only on analysis of about 10% of the total sample library. We contend that full analysis of this sample library could provide insight into the epidemiology and transmission patterns of B. pertussis in ways never before possible. Data from this proposed analysis of the library can answer fundamental questions about asymptomatic carriage, its frequency, and concurrence within the mother/infant pair, and will also be invaluable for updating mathematical models of pertussis transmission, allowing us to answer, for the first time, what proportion of overall pertussis transmission occurs via asymptomatic chains?